This invention relates to a wheel speed sensor-mounting structure for a drum brake.
One known type of a conventional wheel speed sensor-mounting structure is illustrated in FIG. 7. The wheel speed sensor is utilized for an antilock brake system. The structure used in a publicly known duo two leading drum brake will now be described with reference to FIGS. 5-7.
A dust cover 11 closes a bell-house shaped opening of a brake drum (not shown) and is secured to a torque plate 10 on the reverse side thereof by means of shoe-holding pins 20, 21. Each of a number of bolts 30 are force fit through an attachment member, such as the torque plate 10 and/or the dust cover 11, to fix the attachment member to a non-rotatable vehicular portion. Each of the bolts 30 are received by a respective engagement hole 10a of the torque plate 10 at a central portion thereof. Threaded portions of the bolts 30 engage with the non-rotatable vehicular portion, such as an axle casing (not shown), to secure the attachment member thereto in generally coaxial alignment with one another.
In FIG. 5, a pair of wheel cylinders 40, 41 rigidly bolted to the torque plate 10 and dust cover 11 are opened at both ends thereof and also function as anchors for supporting brake shoes 50, 51, positioned between the wheel cylinders 40, 41, at both ends thereof.
The wheel cylinder 40 includes pistons 40a, 40b, while the wheel cylinder 41 includes pistons 41a, 41b. The pistons 40a, 41a are provided with respective manually-operated shoe clearance adjusting mechanisms. In addition, automatically-operated shoe clearance adjusting mechanisms are respectively disposed between the pistons 40a and 40b and between the pistons 41a and 41b. The structure and operation of these two types of the shoe clearance adjusting mechanisms, as well as brake actuation associated therewith, are described in details in published Japanese Utility Model Application Laid-Open No. 1-178242 filed by the present Applicant; therefore, further descriptions related thereto will be omitted.
The brake shoes 50, 51 are comprised of shoe rims 50a, 51a and shoe webs 50b, 51b fixed to form a T-shape in cross-section. The brake shoes 50, 51 also include linings 50c, 51c attached to the shoe rims 50a, 51a on outer peripheral surfaces thereof, respectively. The shoe webs 50b, 51b have respective elongated holes pierced at central portions thereof; and, the shoe-holding pins 20, 21, which extend upward from the torque plate 10, are loosely inserted through the elongated holes. Pairs of slotted nuts 22 screw onto the respective shoe-holding pins 20, 21, thereby permitting respective outer peripheral surfaces of the linings 50c, 51c to be aligned with an inner peripheral surface of the brake drum (not shown), and further holding the brake shoes 50, 51 between the pairs of nuts 22 so as to permit the brake shoes 50, 51 to be slidable in a brake-applying/brake-releasing direction.
The shoe-holding pins 20, 21 are adjusted in the manner described below. Since the upper and lower shoe-holding pins 20, 21 in FIG. 5 are adjusted in the same manner, only the upper shoe-holding pin 20 will be described with reference to FIG. 6. Initially, the slotted nut 22 closer to the torque plate 10 is set on the shoe-holding pin 20 to have a predetermined height from an attached surface of the dust cover 11 mounted to the non-rotatable vehicular portion. Then, the nut 22 is fixed in position by means of a cotter pin 23. Next, the brake shoe 50 is temporally placed on the nut 22 fixed on the shoe-holding pin 20. A second slotted nut 22 disposed on the opposite side of the shoe web 50b from the first slotted nut 22 is fully screwed in, and is then screwed out by a predetermined degree of rotation. In this state, the second nut 22 is fixed in position by means of a respective cotter pin 23, completing the manual operation. Shoe return springs 24, 24 are extended between the brake shoes 50, 51.
A wheel speed sensor 60 (FIGS. 6 and 7) for an antilock brake system (hereafter xe2x80x9cABS wheel speed sensorxe2x80x9d) includes a sensor body 61, a lead wire 62 extending from the sensor body 61 and a bracket 63 for retaining the sensor body 61 in position. As is well known, the ABS wheel speed sensor 60 senses a wheel velocity to control directional stability and steerability of a vehicle, and further to avoid full wheel locking, thereby providing shorter braking distance.
The lead wire 62 extends outside of the drum brake through the torque plate 10 and dust cover 11 and is connected to, e.g., an electronic control unit. The typically cast-molded bracket 63 disposed on the torque plate 10 has a small hole 63a for engaging with a projection 10b of the torque plate 10. In addition, a mounting bolt 64 is screwed into an internal thread 10c of the torque plate 10 through a mounting hole 63b of the bracket 63 from the inside of the drum brake. The bolt 64 fastens the bracket 63 to the torque plate 10 through a spring washer 65. In this state, a top end of the sensor body 61 is positioned to face an outer peripheral surface of a sensor wheel (not shown) with a predetermined gap. The sensor wheel (not shown) is able to rotate together with a rotating axle shaft (not shown).
However, there are problems associated with the above-described prior art wheel speed sensor-mounting structure.
In a drum brake assembly line, when the wheel speed sensor is assembled on the torque plate at either an initial or intermediate process of the assembling, there is a likelihood that the sensor body and lead wire will be damaged when the torque plate having the wheel speed sensor disposed thereon is transferred to subsequent processes, and/or when other components are assembled onto the torque plate.
Accordingly, it is desirable to mount the wheel speed sensor onto the torque plate at the final process of the assembling line. However, space availability for sensor installation is usually limited because of both an inner diameter of the brake drum and the engagement hole of the torque plate at the central portion thereof. In addition, the brake shoes stand in the way. As a result, the assembling sequence as mentioned above is difficult to realize.
For this reason, the brake shoes adjusted in position by means of the shoe-holding pins and the slotted nuts as previously described must be disassembled in order to mount the wheel speed sensor onto the torque plate. The brake shoes are then reassembled after the wheel speed sensor is mounted on the torque plate. Such a laborious operation is inefficient and involves a great deal of effort.
In view of the above, an object of the present invention is to provide a wheel speed sensor-mounting structure for a drum brake, designed to be assembled with significantly less effort, without detracting from qualities of the wheel speed sensor.
In a first aspect, a wheel speed sensor-mounting structure for a drum brake comprises: a wheel speed sensor disposed inside the drum brake on an attachment member fixed to a non-rotatable vehicular portion, the attachment member constituting part of the drum brake, the wheel speed sensor being mounted on the attachment member from outside of the drum brake.
In a second aspect of a wheel speed sensor-mounting structure, the wheel speed sensor bracket has an internal thread defined therein and the attachment member has a mounting hole. A mounting bolt is inserted into the wheel speed sensor through the mounting hole of the attachment member to secure the wheel speed sensor by threading engagement with the internal thread.
In a third aspect of a wheel speed sensor-mounting structure, the wheel speed sensor is formed integrally with a stem extending through the attachment member, and the stem is defined with an external thread. A mounting nut is secured to the stem in threading engagement with the external thread.
In a fourth aspect of a wheel speed sensor-mounting structure, the wheel speed sensor is formed integrally with a stem extending through the attachment member, and a compressed spring is provided between a distal end of the stem and the attachment member.
In a fifth aspect of a wheel speed sensor-mounting structure, a locking means is disposed between the wheel speed sensor and the attachment member for locking the wheel speed sensor against rotation as well as positioning the wheel speed sensor.